1. Field of the Invention
The present invention generally relates to searching for targets in a marine environment and, more particularly, to warning of threats and perils in the marine environment, especially of impending collisions and terrorist threats.
2. Description of the Related Art
An optically-based, marine collision avoidance system was disclosed in my earlier U.S. Pat. No. 4,290,043. A light beam was directed from a transmitter on-board a marine vessel at a surface of the water for refraction into, and also for reflection from, the water. If no obstacle was present in the path of the refracted beam, or in the path of the reflected beam, then the refracted and reflected beams continued their propagation away from the transmitter. If an obstacle was present, then return light reflected off the obstacle by either the impinging refracted beam or the impinging reflected beam was detected by a receiver on-board the vessel, and an alarm was sounded. The light beam included optical radiation having wavelengths in the ultraviolet range (300-400 nanometers) for increased water penetration and/or in the infrared range (700-1500 nanometers) for increased water reflectivity. The light beam had wavelengths transmitted exclusively in one of the ranges, or preferably had wavelengths simultaneously transmitted in both ranges.
As advantageous as my patented collision avoidance system was in warning vessel operators of impending collisions with an obstacle, it provided no information as to the precise location of the obstacle. Thus, my patented system simply warned that an obstacle was present somewhere, but did not advise the vessel operator whether the obstacle was underwater, abovewater, or both. Moreover, my patented system did not advise the vessel operator of the range of a floating or abovewater obstacle, or of the depth of an underwater obstacle. This information would have been helpful in advising the operator how much warning time was available to take evasive action, or if evasive action had to be taken altogether.
Other systems which I am aware include:
U.S. Pat. No. 5,042,942 which discloses the transmission of a laser beam from an overhead, tracking aircraft to an underwater body, especially a towed sled;
U.S. Pat. No. 5,146,287 which discloses an on-board laser scanner to detect floating or submerged hazards, such as mines or torpedoes;
U.S. Pat. No. 5,444,441 which discloses an arrangement for detecting underwater objects by using a camera with three separate arrays of detectors to provide concurrent red, blue and green signals;
U.S. Pat. No. 5,646,907 which discloses detecting floating or submerged objects by transmitting an amplitude-modulated laser beam to the objects, and monitoring for acoustic echoes;
U.S. Pat. No. 3,644,043 which discloses a target search and track system operative, during a search mode, to detect infrared light from the target and, during a track mode, to detect laser light reflected from the target;
U.S. Pat. No. 4,047,816 which discloses the use of two light transceivers to track a vehicle in flight;
U.S. Pat. No. 5,345,304 which discloses a target acquisition system for use on a flight vehicle and employs an infrared detector in combination with a laser sensor;
U.S. Invention Registration H341 which discloses a system for scanning a laser beam at high speed with high resolution, and also at low speed with low resolution to steer a telescope at a target; and
U.S. Invention Registration H1231 which discloses a system for defending against antiship torpedoes by initially employing sonar to determine the approximate location of an incoming torpedo, and by also employing a blue-green laser to scan the located field of view.
Accordingly, it is a general object of the present invention to improve the state of the art as exemplified by U.S. Pat. No. 4,290,043 by distinguishing among underwater targets, abovewater targets, and both abovewater-and-underwater targets.
More particularly, it is an object of the present invention to provide range information as to a distance of an abovewater target relative to a system transmitter.
Still another object of the present invention is to provide depth information as to a distance of an underwater target relative to a system transmitter.
It is yet another object of the present invention to provide both depth and range information of a target, and even to estimate a size of the target.
A still further object of the present invention is to search for human targets in search-and-rescue missions, and in terrorist threats.
Yet another object of the present invention is to search for inanimate targets for collision avoidance.
An additional object of the present invention is to enable system operation twenty-four hours a day, and during different marine conditions.
In keeping with the above objects and others which will become apparent hereafter, one feature of the present invention resides, briefly stated, in a system for, and a method of, searching for targets, both animate and/or inanimate, in a marine environment, comprising a transmitter means, a processor including a receiver means, and an indicator.
The transmitter means is mounted abovewater, for example, on-board a marine vessel, an aircraft, or a seaside structure, such as a pier, a bridge, a marina, or a boat dock. The transmitter means emits first and second beams of optical radiation at first and second zones of water. The first beam has a first wavelength characteristic having wavelengths in the ultraviolet to blue range (300-475 nanometers), hereinafter sometimes referred to as a xe2x80x9cbluexe2x80x9d beam for simplicity, and capable of entering the first zone of water and being refracted therethrough as a refracted beam. The second beam has a second wavelength characteristic having wavelengths in the infrared range (650-1500 nanometers), hereinafter sometimes referred to as a xe2x80x9credxe2x80x9d beam for simplicity, and capable of reflecting from the second zone of water as a reflected beam. The blue and red beams are emitted either by separate transmitters, such as laser light sources, or by a single light source, such as a xenon lamp having means for separating the wide spectrum output of the lamp into separate red and blue beams.
The processor is operative for identifying locations of the targets in the marine environment. The receiver means is operative for separately detecting return target reflections reflected off any targets impinged by the refracted and/or the reflected beams to find an identified target. The return target reflection reflected off a target impinged by the refracted beam, and the return target reflection reflected off a target impinged by the reflected beam, are detected either by separate receivers, or by a single receiver operating in a timewise alternating manner to detect a return target reflection from the refracted beam during one time interval, and to detect a return target reflection from the reflected beam during a subsequent time interval.
The indicator is operative for indicating the identified target. Preferably, the indicator includes a display panel having separate displays for the red and blue beam reflections.
In contrast to the system of my earlier patent described above in which a single beam was propagated forwardly of a vessel, the present invention directs at least two different beams towards at least two different zones of water to obtain two different return target reflections, one by the refracted beam, and another by the reflected beam, and separately detects the return target reflections. If the only target reflection detected is from the refracted beam, then an underwater target is identified. If the only target reflection detected is from the reflected beam, then an abovewater target is identified. If target reflections from both the refracted beam and the reflected beam are detected, then multiple targets are identified, or a single target extending both above and below the water is identified.
In further accordance with this invention, the red and blue beams are pulsed, and the time width of each pulse and the spacing between pulses are known. By determining the time duration from the moment a transmitted pulse is emitted until a corresponding received pulse is detected, the distance or range to a floating or abovewater target can be computed, as well as the depth to an underwater target. The indicator can also display the range and depth information.
Thus, this invention enables targets to be found and categorized with more particularity. Human targets, such as a person requiring rescue, either in a small boat or not, can be identified as a floating target. Terrorists, such as a person or persons intent on causing damage for political purposes, either swimming or being conveyed in a low- or high- profile boat, can be identified as a floating target prior to completing the terrorist mission. Inanimate targets such as floating debris, or seaside structures such as a pier, a dock, a marina, and a bridge, or underwater objects such as a sandbar, a reef or a mine, or abovewater objects such as a bridge support, or objects that extend both above and below the water such as an iceberg, are just a few examples of targets whose depth, range, size and location can be determined by the present invention.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.